Oral implants, after literally centuries of failed efforts, have at last achieved such a degree of success that restoration of functions by means of implants is now a matter of reasonable expectation in a large percentage of patients who have lost teeth. The techniques vary widely, and can generally be categorized in two types: subperiosteal and endosteal.
The subperiosteal implant surmounts the bony structure, with posts rising from it to which a crown or other structure can be attached. The objective of the mounting means is to become attached to the bone, or to be held to the bone by tissue overgrowth. While this type of implant does have some successes, its potential for success, and applicability to many operation conditions are inferior to the potential of the endosteal implant.
The endosteal implant is intended to be inserted into the bony structure, and to be held there by ingrowth of tissue, by osseointegration with the bony structure itself, or by the use of screws or other self-retaining attachment means somehow physically engaged to the bony structure. There have been some considerable successes with endosteal implants, but as they generally exist in the art, their utility is often limited, especially where the bone has been severely reduced.
The inventor in this instant invention has devised a process and an implant which enables an endosteal implant to fit very closely in a natural socket in the jaw, and to be made of a material which is known to result in osteointegration, namely the firm integration of the implant in the bony structure without need for retention means such as expansion bolts, or the like. There results a firmly retained implant with least trauma to the patient, and which becomes as one with the bony structure.
At the present time, there are only two known substances which will be integrated with bony structure: titanium metal and hydroxylapetite. The knowledge that titanium will be osseointegrated has been developed by Branemark, and is now generally accepted. It has led to significantly greater acceptance of oral implants as a conventional practice. Other metals such as gold, and alloys such as vitallium, have had lesser success, and are not believed to be osseointegrated, although they are tolerated by the body.
A body coated with a suitably adherent layer of hydroxylapetite (hereinafter referred to as "HA"), will be retained by osseointegration with the layer of HA. However, should that layer somehow vanish, an implant not made of titanium will suffer the same fate as an implant which was not coated with HA. however, and HA-coated metal implant made of material other than titanium using the process of this invention is intended to be within the scope of this invention.
The known osseointegration of titanium is now so well-established, that prudent practitioners will prefer its use. It can readily be cast in centrifugal casting machines operating in an argon atmosphere. Such machines are in existence, as is sufficiently pure titanium.
It is another object of this invention to provide an implant made of a material which will osseointegrate in a shape corresponding to that of a natural socket in the jaw, and to implant it while the socket is suitably fresh, whereby to return to the socket an implant quite closely correpsonding to the structure --a tooth --which was removed from it.
The idea of replacing an extracted tooth with a cast duplicate has been suggested by Kroder in U.S. Pat. No. 3,628,248. In this patent, Kroder concluded that metal implants could not be used in such a procedure because of the long time it would take to make the implant. By then, he concluded, a membrane he considered necessary to a successful implantation would have disappeared. For this reason, he cast a duplicate of the tooth in a resin and quickly implanted the resinous material. Not only was this material unacceptable, but his basic premise was incorrect. The membrane is largely destroyed anyway when the tooth is extracted. Whatever function it may have had in place with the original tooth, it would not have served for the resin implant. Kroder's procedure has not, to this inventor's knowledge, ever been generally accepted or even used beyond whatever experiments Kroder may have conducted.
When a tooth is first extracted, there remains in the jaw a socket formed of a bony structure most of whose internal surfaces are geometrically similar to the corresponding surfaces of the extracted tooth. In the course of the healing process, a blood clot will form in the socket, and then the blood clot will be invaded by other substances which gradually replace the clot. Then the shape of the surrounding socket structure will begin to change as the materials harden and the shapes are lost. This process takes substantial time, and it appears that no major change of socket shape occurs in the first two weeks after extraction. During this time, when the socket is considered "suitably fresh" for this procedure, the material in the socket can simply be removed with a curette to expose the bony structure. Within this initial period of time, whose maximum length is not presently known, a suitably shaped implant can be pressed into the socket with assurance that it will make surface-to-surface contact with bony structure over an area which, when osseointegrated, will be sufficient to support the implant.
It is not necessary and it cannot be expected to occur, that there will result a 100% area contact of tooth and socket. In fact, it will often be desirable to trim off some roots before making the casting to facilitate later insertion of the implant into the socket. A full area contact of about 30% is believed to be sufficient, and more will obviously be better. At areas where this contact is not made, the interstitial spacing will soon be filled with the same substances as the body provides to heal the socket in normal practice, and does no harm even if it does little good.
Accordingly, it is an object of this invention to provide an endosteal implant which closely conforms to a socket and which will be osseointegrated. This is done without further drilling or structural modification of the socket, and constitutes an important advantage over implants of a specific, often cylindrical, shape, which are implanted in a hole drilled to very close dimensions.